Color television



Aug. 21, 1956 E. J. STERNGLASS 2,760,107

COLOR TELEVISION Filed Oct. 15, 1953 7 l9 ridge Amplifief 23 0T8 u I7 G 45 Delay Line 32 29 Gate I6 e 35 37 Delay Line 33" 3| WITNESSES: INVENTOR Ernest J.Sterng|uss- United States Patent COLOR TELEVISION Ernest J. Sternglass, Pittsburgh, Pa., a'ssignor to Westinghouse Electric Corporation, East Pittsburgh, Pa., a corporation of Pennsylvania Application October 15, 1953, Serial No. 386,281

11 Claims. (Cl. 315-12) This invention relates to cathode ray tubes, and more particularly to improvements therein for obtaining control signals corresponding to the position of the electron beam.

It is an object of this invention to provide an improved cathode ray tube for the reproduction of color television images in natural colors.

It is another object to provide an improved sensing system to generate control signals that are a function of the position of the beam of electrons on a scanning raster of a cathode ray tube.

It is another object to provide an improved system for the reproduction :of color images in which a video signal representing a given component color is applied so as to modulate the intensity of a beam of electrons when the beam of electrons is at a predetermined point on its scanning raster.

It is another object to provide an improved color television tube wherein the electron beam is modulated with video signals at predetermined times by control signals derived from the rear surface of the screen.

It is another object to provide an improved color television tube wherein the electron beam is modulated by a video signal representative of a given component color when the electron beam is at a predetermined point on its scanning raster by control signals derived from primary reflected electrons from the rear surface of the screen.

It is another object to provide an improved method for the depositing of sensing elements on the rear surface of a color television screen.

These and other objects are effected by my invention as will be apparent from the following description taken in accordance with the accompanying drawing throughout which like reference characters indicate like parts, and in which:

Figure 1 illustrates an embodiment of my invention, and

Fig. 2 illustrates a top View of a section of the target or screen employed in the cathode ray tube of Fig. 1.

Referring in detail to Fig. 1, a special type cathode ray tube is provided. The cathode ray tube 10 comprises an evacuated envelope 12 of suitable material, such as glass, having a main chamber in the form of a frustum section 14, a face plate 16 and a neck portion 18. The frusturn section 14 of the envelope 12 contains a target or screen 20 which is deposited on or positioned adjacent to the face plate 16 of the envelope 12. The frus'tum section 14 of the envelope 12 has a collecting electrode 22 in the form of a conducting coating applied on substantially the entire inner surface thereof. The collecting electrode 22 may be of any suitable material of low secondary electron emission such as graphite. Also positioned within the frustum section 14 of envelope 12 is a suppressor grid 24 in the form of a frustum. The suppressor grid 24 is positioned near to, coaxial with and substantially coextensive to the collecting electrode 22. The suppressor grid 24 may be constructed of a wire mesh.

An electron beam source 26 of any suitable type is positioned within the neck portion 18 of the envelope 12 "ice for the generating and projection of an electron beam 13. For the purpose of explanation, I have shown only the cathode 27 and a control grid 25 of the electron gun 26. As is also conventional in television systems, a suitable electrostatic or electromagnetic means is provided for the deflection of the electron beam 13. This deflection means is represented schematically in Fig. 1 by, the deflection coils 28.

A suitable voltage of the order of less than may be applied between the collecting electrode 22 and the suppressor grid 24 by means of a voltage source 30 so that the suppressor grid 24 is at a negative potential with respect to the collecting electrode 22. The collecting electrode 22 and the suppressor grid 24 as well as the screen 2i) are connected to a high voltage source of the order of 12 to 15 kilovolts positive with respect to the potential on the cathode 27.

The screen 20 and the collecting electrode 22 are connected to a bridge circuit 11 by means of the respective connectors 15 and 21. The output of the bridge circuit 11 is connected to a clipper circuit 17 of suitable design. The output of the clipper circuit 17 is connected to a suitable tuned amplifier 19 and the output of the tuned amplifier is connected to a switching circuit 23 directly, and through a delay line 45 to a switching or gating circuit 29 and through a delay line 45 and a second delay line 47 to a switching or gating circiut 31. The video channels 32, 33 and 34 are connected through the switches 23, 29 and 31, respectively, to the control element or grid 25 of the electron source 26.

In the embodiment of the invention which has been selected for illustration, the target of screen 20 comprises a glass or other transparent material foundation which may, as shown in the drawing, be the face plate 16 of the envelope 12. A plurality of parallel groups of phosphor lines 35 are provided on the rear side of the face plate 16. Each group of the phosphor lines 35 includes three strips G, B and R, parallel to each other and extending in a direction so that an electron beam 13 from the electron source will scan the strips G, B and R transversely. The strips G, B and R are comprised of phosphor material capable of emitting light respectively of green, blue and red upon electron bombardment by the electron beam 13. There are several suitable phosphors available, for exam-' ple zinc phosphate activated with manganese for the red lines R, Zinc silicate activated by manganese for the green lines G and zinc sulfide activated with silver for the blue lines B. The phosphor strips G, B and R may be applied to the face plate 16 in any suitable manner, for example by the silk screening method.

After the phosphor strips G, B and R have been applied to the face plate 16, a thin metallic film 36 is deposited next in the form of a smooth surface on the rear side of the phosphor strips G, B and R by means well known in the art. The metallic film 36 is sufficiently thin and of suitable material so as to be electron permeable to permit most of the incident primary electrons from the electron beam 13 to penetrate into the phosphor strips G, B and R. The metallic film 36 serves not only as a reflector of light from the phosphor strips G, B and R, but also as a back scatterer of some of the electrons and as the high voltage electrode. An example of a suitable material is gold for the layer 36 which also has the heme ficial property of being an excellent reflector for red light, which is generally the least intensive phosphor now available. Gold has an additional property which is beneficial to my invention, in that it is insensitive to small amounts of surface impurities which might effect the remay be desirable to omit the film 36 in some applications. It may be necessary if the metallic film 36 is omitted to utilize a conductive transparent material as the foundation member 16, such as Nesa.

A plurality of sensing film strips 37 are deposited onto the rear side of the metallic film 36. The material that comprises the sensing strips 37 is of a suitable material that is permeable to electrons from the electron beam 13 and having widely difierent coeflicient of reflection of incident electrons and secondary emission than the metallic film 36. An example of a suitable material is amorphous carbon which would reduce the coeflicient of reflection of incident electrons and secondary emission, as compared to the metallic film 36 comprised of gold. For example,

as described here, the sensing strips 37 would reduce the number of reflected incident electrons and secondary emission from the metallic film 36, but it is Within the scope of my invention that a material such as nickel may be utilized for the sensing strip 37 of a higher yield of reflected incident electrons and secondary emitted electrons than the metallic film 36 such as aluminum. The amorphous carbon utilized in the sensing strips 37 also possesses the advantage of insensitivity to small amounts of contamination. The amorphous carbon or nickel sensing strips 37 and the aluminum or gold film 36 have the property of stability of yield as to reflected incident electrons and secondary emitted electrons under a prolonged bombardment by the electron beam 13 as compared to the materials such as phosphor crystals utilized in the phosphor strips G, B and R.

The preferred method of depositing the sensing strip 37 rests on the fact that complex molecules such as those of organic oils, metal-carbonyls and cyanides may be decomposed or cracked by the action of an electron beam leaving a residue of one of the molecular constituents behind, which is confined to the region Where the beam strikes the surface. In the case of the metal-carbonyls and cyanides the metallic atoms are deposited out while in the case of the oil the carbon is deposited as an amorphous film. When an electron beam of the energy of a few hundred to a few thousand volts impinges on a metallic surface, such as gold, in the presence of oil vapors, such as that produced from a commercial product sold under the trade name Octoil, a layer of amorphous carbon is gradually built up in the region where the electron beam strikes the metallic surface. The resulting deposits have been found to be nearly pure carbon. The thickness of the deposit may be controlled most satisfactorily by varying the electron beam current or the time of bombardment.

In one embodiment of my invention, after the metallic film is deposited, the envelope 12 is connected to a vacuum system, not shown, and exhausted suficiently to permit operation of the electron gun. The Octoil may be admitted into the envelope 12. The position of the electron beam 13 is adjusted until the color of the phosphor strip G, B or R appears, onto the rear side of which it is desired to deposit the amorphous carbon sensing strip 37. Since the G and B strips containing the green and blue light emitting phosphors are more sensitive than the R strip, the sensing strip may be deposited on either G or B, and I have utilized the G strip. It is also usually desirable to deposit a sensing strip behind the G strip of each group of phosphor strips G, B and R. It is within the scope of my invention that various arrangements and position of the sensing strips may be utilized with proper control means.

After determining the desired sensing arrangement, the electron beam 13 is moved at the desired speed along the G phosphor strip. A photoelectrically operated control system of suitable design may be utilized to keep the electron beam 13 on as long as the desired color G is observed. The oil vapor admitted to the envelope 12 is cracked only when the electron beam is focused on the desired color strip G. This procedure or method of depositing the sensing strips results in sensing strips deposited parallel to and in exact coincidence with the desired phosphor strip G in each group of phosphors G, B and R.

Instead of depositing a material of a higher or lower reflected incident and secondary emission electron yield, on the metallic layer, it may be desirable to deposit different thicknesses of a given material such as nickel from a carbonyl vapor directly onto the phosphor strips G, B and R and omit the separately deposited metallic film 36. The difl'erent thickness will scatter back different fractions of the incident electrons.

The operation of the tube and (one possible form of) associated circuitry may be described as follows. The electron beam 13 produced by the electron source scans a raster on the screen 20 by means of a signal received from a suitable receiver and applied to the deflection coils 2.8. The electron beam 13 is caused to scan transversely the phosphor strips R, G and B. The electron source 26 is biased so that when no video information is applied, there will be a small electron beam current. This low value of electron beam current must be suflicient that on striking the exposed area of the metallic film 36, suflicient signal will be developed to energize the control system. As the electron beam 13 scans across the phosphor strips G, B and R, pulsating direct current will be obtained from the collector 22 or screen 20 with the video signal superimposed thereon. The video signal may be removed by coupling the signal from the screen 20 and the collecting electrode to the bridge circuit 11 where the video signal is removed from the composite signal derived from the collecting electrode 22 and screen 20.

The signal derived from the bridge circuit 11 represents the difiference in reflected incident electrons due to the difference in reflection of the metallic layer 36 and the sensing strips 37. As the electron beam 13 scans across the screen 20, a number of the reflected incident electrons 20 from the electron beam 13 are reflected and also secondary electrons 41 are emitted from the exposed surface of the metallic layer 36 while a ditferent number will be obtained from the sensing strip 37 deposited on the phosphor strip G.

It is understood that electrons leaving the screen 20 as result of the electron bombardment by the primary electrons within the beam 13 are of two types i. e., those having an energy of less than 50 electron volts are considered secondary emitted electrons while those electrons having an energy of more than 50 electron volts and less than the energy of the primary electrons within the beam 13 are considered reflected incident or primary electrons. Since the low energy secondary electrons 41 do not have sufiicient energy to overcome the negative potential applied between the suppressor grid 24 and collecting electrode 22, these electrons 41 will be returned to the screen 20. The reflected incident electrons 40 are of suflicient energy to overcome the negative potential applied between the suppressor grid 24 and collecting electrode 22 and are collected on the collecting electrode 22. It is also possible to apply additional voltages to the suppressor grid 24 of the order of volts and to the collecting electrode 22 of the order of 50 volts, both positive with respect to the screen 20. In this manner both the reflected incident electronsland secondary electrons are utilized for the sensing s1gna With the video signal removed, the reflected incident electron pulsations are equivalent to the pulsation response from a constant electron gun current. Therefore, the number of reflected incident electrons from the R and B strips covered by the metallic layer 36 will be of the same number While a reduced number of reflected incident electrons will be received from the G strip which is covered by a sensing strip 37.

The signal derived from the clipper circuit 17 is fed to a suitable tuned amplifier 19. The output of the tuned amplifier 19 is fed directly to the gate 23 and also to the delay lines 45 and 47 so as to produce an immediate pulse and two delayed pulses of different delay time. These three pulses are applied respectively to the switches 23, 29 and 31 so as to gate the video channels sequentially at a predetermined time or place on the scanning raster so that the proper video information will be applied to the electron source 26 when the electron beam 13 is substantially positioned upon the proper phosphor strip R, G or B.

In another embodiment of my invention, the metallic layer may be omitted and the sensing strip film 37 applied to all phosphor strips G, B and R with a different thickness on one of the strips G, B or R.

Another possible modification would be the use of sensing strip 37 on one strip, for example G, and leave the other phosphor strip R and B exposed.

A table showing the secondary emission and reflected incident electrons from five materials at two and fifteen kilovolts incident electron energy is presented below. It is seen that the difference in secondary emission between different material is small at fifteen kilovolts, while a large difference may be obtained with the reflected incident electrons.

Table of yields from typical materials at 2 and 15 While I have shown my invention in several forms, it will be obvious to those skilled in the art that it is not so limited, but is susceptible of various other changes and modifications without departing from the spirit and scope thereof.

I claim as my invention:

1. An electron sensitive color target comprising a foundation having a plurality of groups of elemental areas, each of said elemental areas comprising a phosphor material capable of emitting light on electron bombardment of a color independent to that area, an electron permeable light reflecting layer of a material of high atomic number supported upon said groups of phosphor coated elemental areas, a plurality of electron permeable coatings of a material of low atomic number disposed on said layer, each in registry with a selected elemental color phosphor area, and collecting means for deriving a signal representative of reflected electrons from said target.

2. A color television tube comprising an evacuated envelope having a screen disposed therein, said screen comprising a foundation having a plurality of groups of phosphor strips, each of said groups having a strip representative of a selected component color, an electron permeable light reflecting layer of a material of high atomic number supported upon said groups of phosphor strips, a plurality of electron permeable sensing strips of a material of low atomic number disposed on said light reflecting layer each in registry with a particular one of the phosphor strips representative of one of the selected component colors of each group, electron beam scanning means for scanning said screen transversely to said phosphor strips, and col lecting means for deriving a signal representative of the reflected primary electrons from said screen.

3. In combination a cathode ray tube comprising an evacuated envelope, a screen positioned within said envelope adjacent one end thereof, said screen comprising a supporting layer, a plurality of groups of phosphor strips on the rear surface of said supporting layer, each of said groups of phosphor strips comprising a plurality of strips capable of emission of light of different selected component colors upon electron bombardment, a plurality of sensing strips of an electron permeable material on the rear surface of said phosphor strips in registration with selected phosphor strips and of a material having a different coefficient of incident electron reflection than said phosphor surface, means for scanning said screen transversely to said phosphor strips, and means for collecting the reflected electrons from said screen, said means comprising a collecting surface of a material of low secondary electron emission.

4. In combination a cathode ray tube comprising an evacuated envelope, a screen positioned within said envelope at one thereof, said screen comprising a supporting layer, a plurality of groups of phosphor strips on the rear surface of said supporting layer, each of said groups of phosphor strips comprising a plurality of strips capable of emission of light of different selected component colors upon electron bombardment, a sensing layer of a material of a different coefficient of secondary electron emission than said phosphor strips, disposed on the rear of said phosphor strips in a predetermined registration arrangement, means comprising a coating on a portion of the interior surface of said envelope for collecting secondary electrons from said screen and means for suppressing the secondary emission from said coating.

5. In combination a cathode ray tube comprising an evacuated envelope, a screen positioned within said envelope at one end thereof, said screen comprising a supporting layer, a plurality of groups of phosphor strips on the rear surface of said supporting layer, each of said groups of phosphor strips comprising a plurality of strips capable of emission of light of different selected component colors upon electron bombardment, a metallic layer of an electron permeable material disposed on the rear of said phosphor strips, sensing strips disposed on the rear of said metallic layer, said sensing strips having a different ratio of reflection of incident electrons than said metallic layer, means comprising a conductive coating on a portion of the interior surface of said envelope, and a suppressor grid near to and substantially coextensive with said conductive coating for collecting the reflected incident electrons and repelling secondary emitted electrons for said screen and means for scanning an electron beam transversely to said phosphor strips.

6. In combination a cathode ray tube comprising an evacuated envelope, a screen positioned Within said envelope at one end thereof, said screen comprising a supporting layer, a plurality of groups of phosphor strips on the rear surface of said supporting layer, each of said groups of phosphor strips comprising a plurality of strips capable of emission of light of different selected component colors upon electron bombardment, a metallic layer of an electron permeable material capable of reflecting a portion of the incident electrons disposed on the rear of said phosphor strips, a plurality of sensing strips disposed on the rear of said metallic layer in registration with selected strips of said phosphor material, said sensing strips being of a material having a different ratio of reflection of incident electrons than said metallic layer, means for collecting said reflected incident electrons comprising a coating on the interior portion of said envelope, a suppressor grid near to and substantially coextensive to said conductive coating, means of applying a suitable voltage difference between said conductive coating and said suppressor grid so as to collect incident reflected electrons and repel secondary emission electrons back to said screen, and means for scanning an electron raster upon said screen.

7. In combination a cathode ray tube comprising an evacuated envelope, a screen positioned within said envelope adjacent one end thereof, said screen comprising a supporting layer, a plurality of groups of phosphor strips on the rear of said supporting layer, each of said groups of phosphor strips comprising a plurality of strips capable of emission of light of different selected component colors upon electron bombardment, a sensing layer disposed on the rear of said phosphor strips, said sensing layer having a predetermined thickness in the rear of and in registration with One of the selected component color strips While a diflerent thickness is provided to the rear of the others of said phosphor strips, means for collecting the reflected incident electrons from said screen, circuit means for utilizing diflerences in said reflected incident electron current to gate said electron beam with video information and means for scanning said electron beam transversely to said phosphor strips.

8. In combination a cathode ray tube comprising an evacuated envelope, a screen positioned at one end of said envelope, a conductive coating with an external connection on a substantial portion of the interior surface of said envelope, a suppressor grid placed near to and substantially coextensive with said conductive coating and means for scanning said screen with an electron beam.

9. A color television tube comprising an evacuated envelope having an image screen deposited therein, said image screen comprising a plurality of groups of phosphor coated strips, each of said groups having a strip representative of a selected component color, an electron permeable light reflecting layer supported upon said group of phosphor strips, an electron gun positioned within said envelope for scanning a raster on said image screen, a plurality of electron permeable sensing strips disposed on said light reflecting layer, said sensing strips being deposited in registration with selected phosphor strips, said sensing strips having a different coefiicient of incident electron reflection than said phosphor strips, and means for measuring the incident electron reflection from said image screen, said means comprising a collecting electrode and suppressor electrode.

10. A color television tube comprising an evacuated envelope having an image screen deposited therein, said image screen comprising a foundation having a plurality of groups of phosphor coated strips, each of said groups having a strip representative of a selected component color, an electron permeable light reflecting layer supported upon said group of phosphor strips, an electron gun positioned within said envelope for scanning a raster on said image screen, a plurality of electron permeable sensing strips disposed on said light reflecting layer, said electron permeable strips comprising a layer of amorphous carbon in registration with only the selected phosphor strips, said amorphous carbon sensing strips having a dilferent coeflicient of incident electron reflection than said light reflecting layer, means for collecting the re flected incident electrons from said image screen, and means for utilizing said reflected incident electrons to control the speed of scan of said electron beam.

ll. In combination a cathode ray tube comprising an evacuated envelope, and having therein, means for generating an electron beam, a screen positioned Within said envelope at one end thereof, said screen comprising a supporting layer, a plurality of groups of phosphor strips on the rear surface of said supporting layer, each of said groups of phosphor strips comprising a plurality of strips capable of emission of light of different selected component colors upon electron bombardment, a metallic layer of electron permeable material disposed on the rear of said phosphor strips, sensing elements disposed on the rear surface of said screen, said sensing strips having a diflerent ratio of reflection of incident electrons than said metallic layer, a conductive coating on a portion of the interior surface of said envelope and a suppressing member for suppressing secondary emission from said conductive coating, means for deriving a signal from said conductive coating and said screen representative of reflected incident electrons from said screen and free of video modulation on said beam, and means for deflecting said electron beam transversely to said phosphor strips.

References Cited in the file of this patent UNITED STATES PATENTS 2,631,259 Nicoll Mar. 10, 1953 2,644,855 Bradley July 7, 1953 2,657,331 Parker Oct. 27, 1953 2,667,534 Creamer et a1. Jan. 26, 1954 2,671,129 Moore Mar. 2, 1954 2,689,269 Bradley Sept. 14, 1954 2,689,927 Bradley Sept. 21, 1954 

